From the Guidelines
Ondansetron (Zofran) is not recommended for use as an antihistamine. Ondansetron is a 5-HT3 receptor antagonist primarily used to prevent nausea and vomiting associated with chemotherapy, radiation therapy, and surgery. It works by blocking serotonin receptors in the brain and gut, which helps control the vomiting reflex. Unlike true antihistamines such as diphenhydramine (Benadryl) or cetirizine (Zyrtec), ondansetron does not block histamine H1 receptors, which are responsible for allergy symptoms like itching, sneezing, and hives. Therefore, ondansetron would not be effective for treating allergic reactions or conditions where antihistamines are typically prescribed. If you need an antihistamine for allergies or allergic reactions, medications specifically designed as antihistamines should be used instead. The confusion may arise because some antihistamines like promethazine also have anti-nausea properties, but ondansetron works through an entirely different mechanism and lacks antihistamine activity.
Key Points
- Ondansetron is a 5-HT3 receptor antagonist, not an antihistamine 1
- It is used to prevent nausea and vomiting associated with chemotherapy, radiation therapy, and surgery
- Ondansetron does not block histamine H1 receptors, which are responsible for allergy symptoms
- Medications specifically designed as antihistamines should be used for allergies or allergic reactions
Evidence
The most recent and highest quality study, published in 2017, does not support the use of ondansetron as an antihistamine 1. This study, along with others, confirms that ondansetron is effective in preventing nausea and vomiting associated with chemotherapy and radiation therapy, but it does not have antihistamine properties. Other studies, such as those published in 2008,2009,2010, and 2017, also support this conclusion 1.
Recommendation
Ondansetron should not be used as an antihistamine. Instead, medications specifically designed as antihistamines, such as diphenhydramine or cetirizine, should be used to treat allergic reactions or conditions where antihistamines are typically prescribed.
From the Research
Ondansetron as an Anti-Histamine
- Ondansetron is a selective 5-HT3 receptor antagonist, primarily used for its antiemetic properties in preventing nausea and vomiting caused by chemotherapy, radiotherapy, and surgery 2, 3.
- There is no evidence to suggest that ondansetron is used as an anti-histamine. Anti-histamines, such as H1-antihistamines, are used to treat allergic diseases by inactivating the histamine H1-receptor 4.
- Ondansetron's mechanism of action is distinct from that of anti-histamines, and it is not classified as an anti-histamine 2, 3.
- While ondansetron has been associated with hypersensitivity reactions, including urticaria, this is not indicative of its use as an anti-histamine, but rather a potential adverse effect of the drug 5.
- In the treatment of nausea and vomiting, ondansetron is often used in conjunction with other medications, including anti-histamines like diphenhydramine, but it is not a replacement for anti-histamines in the treatment of allergic diseases 2, 6.